This invention relates to a method and an apparatus for recording on and reproducing from a magnetic disk having its recording area divided into a plurality of sectors, each sector including an ID area and a data area, and more particularly to a method for recording on or reproducing from a magnetic disk, which method contributes to increasing the access speed.
This invention relates to a magnetic recording and reproducing apparatus for recording on a magnetic disk having a plurality of divided recording areas, each divided recording area including an identification area and a data area, and more particularly to a magnetic recording and reproducing apparatus, a control circuit for the magnetic recording and reproducing apparatus and a magnetic recording and reproducing method, which are most suitable for magnetic recording and reproduction with a dual head (hereafter referred to the dual head) combining a reproducing head, such as an MR (magneto-resistive effect) head and a recording head.
The bit error rate of data transferred from a magnetic disk unit to a computer is generally desired to be 1.0E-14 or less. However, it is virtually impossible to keep the bit error rate of data read from the magnetic disk at a level of this order. Therefore, normally, redundant bits for error check or error correction are added to record data, and a magnetic disk controller (hereafter referred to as the controller), provided between the magnetic disk unit and the computer, is used to detect or correct errors of data which is read by the controller so as to limit the bit error rate of data from the controller to the computer to 1.0E-14 or less even when the tolerance limit for the bit error rate of data from the magnetic disk unit is about 1.0E-9. Incidentally, in view of the error correction capability of the controller, it is possible to further tolerate the bit error rate of data read by the controller. If more errors can be tolerated in accordance with the difference between the current bit error rate and the deteriorate bit error rate, for example from the current 1.0E-9 to 1.0E-6, in compliance with an increase in the so-called window margin, the recording density, or the recording capacity of the magnetic disk can be increased. However, as the bit error rate is deteriorate, the greater number of times error bits are corrected. If the correction process time for one error is long, a large overhead for the error correction process causes the performance of the apparatus to deteriorate. Heretofore, there has been a problem that correcting errors takes time for the reason described below, and after all, the bit error rate of data read from the magnetic disk into the controller cannot be improved. Specifically, the magnetic disk is normally divided into a plurality of sectors for a more effective access. FIG. 2 shows a recording format for each of the sectors 1, 2, . . . The sectors 1, 2, . . . are divided into the ID areas, ID0, ID1, ID2, . . . and the data areas DATA0, DATA1, DATA2, . . . . The data areas ID0, ID1, ID2, . . . are each divided into information PROSYNC for phase synchronization of a PLL (phase lock loop), AM indicating the leading end of the ID area, C for a cylinder number of data, H for a head number of data, S for a sector number of data, CRC indicating whether or not an error has occurred, and ID PAD indicating a border between the ID area and the data area. Recording or reproduction of the record format on a data area of the magnetic disk is executed after information of the ID area of the same sector is verified. Error detection of the ID information is performed by comparing an error check code generated by using the ID information which has been read and an error check code CRC recorded in advance. This error detection can be done at high speed, but if an error is detected, data has to be read again (by retry), for which a waiting time for one rotation of the disk is required. In order to solve this problem, it has been proposed to correct errors in the information of the ID area by adding an error correcting code to the ID area as disclosed in JP-A-63-86160 (Prior Art 1). However, the conventional method for error correction takes time. Unless the error correction of the ID area is finished by the time data is written in the data area specified by the ID, a disk rotational delay occurs. To avoid this problem, there has been proposed a method for placing the corresponding ID areas and data areas in different sectors instead of placing in the same sectors to thereby secure time for correcting errors, as shown in FIGS. 3A to 3D.
In the past, magnetic heads, such as the inductive head or the MIG (Metal In Gap) head capable of both reading and writing, were used to read data from or write onto the magnetic disk unit.
Recently, dual heads, containing a magnetic head for writing (inductive, MIG, etc.) and a magnetic head for reading, are mounted. In addition, an MR (Magneto-Resistive) head, which is not dependent on the rotating speed of the disk and which is compatible with small disks, has began to be used for the magnetic head for reading.
The dual head as described has a problem that because it is generally manufactured in a monolithic body including the writing head and the reading head, a discordance occurs invariably between the core centers of the two heads in the manufacturing process.
According to a technique revealed in JP-A-3-160675, in the magnetic disk unit using a dual head, servo information is provided separately for writing and reading in the areas on the magnetic disk which are shifted with respect to each other by the amount equal to the distance of a radial shift between with the reading head and the writing head, and under this head configuration, data can be written into the data area without moving the magnetic head. (See FIG. 38.) Though not disclosed in the above-mentioned patent publication, the format pattern that the inventors presumed from the description of the patent publication is shown in FIGS. 39A to 39C. Description will now be made of W.SPLICE. When writing data, it is confirmed by reading information in the ID area whether or not an object sector is accessed reading information of the ID area and the magnetic head unit writes data in the next area. It is necessary to gain time from this reading until the electronic circuit for writing becomes ready for operation. The area provided for gaining this time is W.SPLICE.
An object of the present invention is to provide a high-speed error correction method wherein correction of an error in the ID area can be finished by the time data is written in the data area specified by the ID information provided physically in the same sector, and the corresponding ID area and data area can be placed in the same sector.
A second object of the present invention is to provide a magnetic recording and reproducing apparatus which uses a dual head and finishes error correction of the identification information by the time of starting writing data into the data area corresponding to the identification information placed in the same recording area.
A third object of the present invention is to provide a magnetic recording and reproducing apparatus which uses a dual head, decodes coded data, such as maximum likelihood decoding, and which is free from a decrease in formatting efficiency.
A fourth object of the present invention is to provide a large-capacity small-size disk-type recording and reproducing apparatus which uses a dual head.
A fifth object of the present invention is to provide a disk-type recording and reproducing apparatus which uses a dual head and which is capable of high-speed formatting.
The above-mentioned object of the present invention (hereafter referred to as the first object) will be described.
The above-mentioned prior art has a problem that since the corresponding ID area and data area are not set in the same sector but are set in the physically different sectors, so that the control operation of the controller is complicated and malfunctioning is liable to occur.
In order to achieve the above-mentioned first object, a first means is provided by which to finish error correction in the ID area before data is read from or written into the data area corresponding to the ID area. More specifically, there is provided means whereby when an expected value of the ID of the sector where information is to be read or written, added with an expected value of an error correcting code calculated from the expected value of the ID, is compared with a value actually read from the magnetic disk, if the discordant quantity of data exceeds the correctable quantity of data, the expected value of the ID and the read-out value are regarded as discordant.
Further, to achieve the first object, a second means is provided by which to finish the error correction of the ID area before data is read from or written into the data area corresponding to the ID area. To be more specific, when an expected value of the ID in the sector where information is to be read or written, added with an expected value of an error correcting code calculated from the expected value of the ID is compared with a value actually read from the magnetic disk, if the discordant quantity of data does not exceed the correctable quantity of data, the expected value of the ID and the read-out value are regarded as accordant.
Further, to achieve the first object, there is provided a third means by which to finish the error correction of the ID area before data is read from or written into the data area corresponding to the ID area. To be more specific, an error correcting code in the ID area is formed by being interleaved with a Hamming code, for example, which is instantly correctable and relatively short and simple.
Further, to achieve the first object, as a fourth means, the error correcting code in the ID area is arranged to have the same value as in the ID area.
In the first means, when an expected value of the ID of the sector where information is to be read or written, added with an expected value of the error correcting code calculated from the expected value of the ID, is compared with a value actually read from the magnetic disk, if the discordant quantity of data exceeds the correctable quantity t of data, the expected value of the ID and the read-out value are regarded as discordant. According to the coding theory, the t symbol error correcting code should have the minimum Hamming distance of 2t+1 or more, and the distance from one code to another should be 2t+1 symbols or more. Therefore, data which, after corrected, can accord with a code including the expected value of the ID and the expected value of the error correcting code is never corrected erroneously to other data and regarded as a discordant data. In addition, an accord/discord decision can be made taking into account a result of correction when the last data is read, and therefore, even if a data area corresponding to an ID area is placed just behind the ID area, data can be read from or written in the data area corresponding to the ID area after the value in the ID area has been corrected by ECC.
In the second means, when an expected value of the ID in a sector where information is to be read or written, added with an expected value of the error correcting code calculated from the expected value of the ID is compared with a value actually read from the magnetic disk, if the discordant quantity of data does not exceed a correctable quantity of data, the value of the ID and the read value are regarded as accordant. According to the coding theory, the t symbol error correcting code should have the minimum Hamming distance of 2t+1 or more, data which, after corrected, can accord with a code including the expected value of the ID and the expected value of the error correcting code is never corrected erroneously to other data and regarded a discordant data. In addition, an accord/discord decision can be made taking into account a result of correction when the last data has been read, and therefore, even if a data area corresponding to an ID area is placed just behind the ID area, data can be read from or written in the data area corresponding to the ID area after the value in the ID area has been corrected by ECC.
In the third means, an error correcting code of the ID area is formed by being interleaved with a Hamming code, for example, which is instantly correctable. Since an accord/discord decision can be made taking into account a result of correction when the last data has been read, and therefore, even if a data area corresponding to an ID area is placed just behind the ID area, data can be read from or written in the data area corresponding to the ID area after the value in the ID area has been corrected by ECC.
In the fourth means, an arrangement is made so that the error correcting code of the ID area has the same value as the value of the ID area, and that when either one or both of the ID agrees with the value read from the magnetic disk, a decision is made that two compared values are regarded as accordant. Even if either one ID cannot be read in a normal manner, an accord/discord decision is made when the last data is read. Therefore, even if a data area corresponding to the ID area is placed just behind the ID area, data can be read from or written in the data area corresponding to the ID area.
According to the present invention, even when a data area corresponding to the ID area is placed just behind the ID area, data can be read from or written in the data area corresponding to the ID area by finishing an error correction of the ID area by ECC without a rotational delay, so that even with a system of a high bit error rate, a read/write operation can be conducted on the data area without increasing the access time and furthermore, the control operation by the controller does not become complicated.
The second and third objects of the present invention will be described. A technique which uses a dual head is disclosed in Japanese Patent Application No. 3-254953, the contents of which will be described with reference to FIG. 16.
FIG. 20 is a schematic diagram showing a track format. The ID division 3002 in the Figure corresponds to the ID area mentioned above. As shown in the Figure, an ID division 3002 includes two ID divisions 3002-1 and 3002-2, in which the same contents are written as in the conventional magnetic disk. The two ID divisions 3002-1 and 3002-2 are shifted with respect to each other by the amount of shift (xcex4) between the recording head and the reproducing head. At track No. N, by using a servo signal division set before the ID division 3002 (at this time, the center line of the servo signal division is supposed to coincide with the center line of the recording head), the recording head 3005 is positioned to the center line of writing (the data division), and under this condition, the recording ID division 3002-2 is reproduced (read) by the reproducing head 3004. At track No. N+1, by use of the servo signal division, the center lines are set offset by xcex4, with the result that the reproducing head 3004 is positioned to the center line of reading (the reproducing ID division and the data division). In this case, the reproducing ID division 3002-1 is reproduced and the data division 3003 is reproduced. In the manner as described, by selectively using the two ID divisions 3002-1 and 3002-2, even if the positions of the heads are changed between the recording and reproducing operations, the ID divisions can be detected without any positional shift at all times.
As mentioned in the description of the prior art, it has been proposed to add an error correcting code (ECC) also to the ID area to correct errors in information in the ID area. However, in the prior art, the corresponding ID area and data area are not placed in the same sector but in physically different sectors, which results in problems that the control operation of the controller is complicated and malfunctioning is liable to occur.
Also in the technique described in Japanese Patent Application No. 3-254953, unless error correction of the recording ID area is finished by the time data starts to be written into the data area corresponding to the recording ID area, the recording head passes the leading end of the writing area, so that it becomes necessary to wait for the head to complete one rotation, thus producing a rotational delay time. For this reason, a gap needs to be provided just behind the recording ID area.
The foregoing process takes place after the signal read by the head has been decoded to reproduce a digital value. With regard to decoding, as shown in Nikkei Electronics 1991, 9, 30 pp. 77-106, it has been proposed to combine an MR head, which is a read-only head, and the maximum likelihood decoding (Viterbi decoding) in order to improve reliability of data. However, a problem with this technique is that the maximum likelihood decoding (Viterbi decoding) requires a long decoding time, and therefore, the data area cannot be placed just behind the ID area, with the result that the formatting efficiency deteriorates.
The second and third objects of the present invention are to solve the above-mentioned problems.
In order to achieve the second and third objects of the present invention, there is provided a magnetic recording and reproducing apparatus for magnetically recording and reproducing on a magnetic disk with a dual head including separate recording and reproducing heads, wherein the recording area on the magnetic disk is divided into a plurality of recording areas, each divided recording area including an identification area having recorded therein information for identifying the divided recording area, wherein the identification area is further divided into an identification area for recording, used when recording, and an identification area for reproduction, used when reproducing, wherein there is provided read-out means for reading identification information from the identification area for recording when recording and reading identification information from the identification area for reproduction when reproducing, and wherein in the same divided recording area, an identification area for reproduction is placed between an identification area for recording and a data area.
Further, the identification area for reproduction has an error correcting code, and the magnetic recording and reproducing apparatus comprises identification information memory means for storing identification information supplied from outside to specify the data area where data is to be reproduced; data memory means for processing on a first-in first-out basis reproduced data from a magnetic disk; a data buffer for storing data output from the data memory means; error correcting means for correcting errors in the identification information for reproduction, read from the magnetic disk, by the error correcting code, and outputting a xe2x80x9cnot correctablexe2x80x9d signal when error correction is impossible; and data transfer control means for transferring data stored in the data memory means to the data buffer when the error-corrected identification information for reproduction, accords with the identification information supplied from outside, and not transferring data to the data buffer when the error-corrected identification information for reproduction does not accords with the identification information supplied from outside or when a xe2x80x9cnot correctablexe2x80x9d signal is received.
Further, the identification area for reproduction has an error correcting code, and the magnetic recording and reproducing apparatus comprises identification information memory means for storing identification information supplied from outside to specify the data area where data is to be reproduced; a data buffer for storing reproduced data read from the magnetic disk; error correcting means for correcting errors in the identification information for reproduction, read from the magnetic disk, by the error correcting code, and outputting a xe2x80x9cnot correctablexe2x80x9d signal when error correction is impossible; and data invalidating means for invalidating the data transferred to the data buffer when the error-corrected identification information for reproduction does not accord with the identification information for reproduction supplied from outside or when a xe2x80x9cnot correctablexe2x80x9d signal is received.
Further, decoding the identification information for recording is conducted while the magnetic head passes the identification area for reproduction and is finished before data is to be written into the data area corresponding to the identification area for recording.
Further, the identification information for reproduction and data are recorded respectively in the identification area for reproduction and the data area without having intervene between those areas at least any one of a data area indicating a border between the identification area for reproduction and the data area, a gap area between the identification area for reproduction and the data area, a synchronization pattern area, and an area indicating a leading end of the data area.
Further, formatting means is provided by which when formatting, identification information for recording is written during the first rotation, then the written identification information for recording is reproduced during the second rotation, and if the information has been written correctly, during the same rotation, identification information for reproduction is written just behind the identification information for recording.
In the present invention, identification information for recording is added with an error correcting code, the identification area for recording is placed ahead of the identification information area for reproduction, and after the identification information for recording is read, while the magnetic head passes the identification area for reproduction, error detection and correction of the identification information for recording are finished, and therefore, after errors of the identification area for recording have been corrected, data can be written in the data area corresponding to the recording identification area. If error correction of the identification information for recording has failed, or if the recording identification information that has been read differs from what is expected, writing data is terminated, so that data is prevented from being written into a wrong sector.
After the identification information for reproduction has been read, error detection and correction of the identification information for reproduction is conducted, and data which has been read during the error detection and correction of the identification information for reproduction is stored in an FIFO (first-in first-out) memory (the data memory means for processing on a first-in first-out basis), and after the error correction is finished, if the identification information is determined to be information of the object sector, the data in the FIFO unit is transferred to the data buffer for storing data to be sent to the host computer, or if error correction is impossible or the error-corrected identification information is determined not to be information of the object sector, the data in the FIFO unit is invalidated, so that the data area corresponding to the above-mentioned identification area can be read, and wrong data is not transferred to the host computer.
Further, after the identification information for reproduction has been read, error detection and correction of the identification information for reproduction is conducted, and data which has been read during the error detection and correction of the identification information for reproduction is sent to the data buffer, when error correction is impossible or the error-corrected identification information is determined not to be information of the object sector, the data in the data buffer is invalidated, so that the data area corresponding to the above-mentioned identification area can be read, and wrong data is not transferred to the host computer.
Further, in the present invention, since the identification area for recording is placed ahead of the identification area for reproduction, after the identification information for recording is read, Viterbi decoding of the identification information for recording can be executed and finished while the magnetic head passes the identification area for reproduction, and it is not necessary to provide an idle area to gain time for Viterbi coding and correction between the identification area for recording and the data area, with the result that the formatting efficiency is improved.
Further, an identification area for reproduction and a data area are successively placed behind one gap and a synchronization pattern area, so that the gap, the synchronization pattern, etc. which are provided conventionally, can be omitted, and the decrease of the formatting efficiency attributable to the increase to the two identification areas can be reduced.
Further, when formatting, identification information for recording is written during the first rotation, the identification information for recording is read during the next rotation, and after the identification information is compared with its expected value and if its adequacy is verified, identification information for reproduction is written during the same rotation. For this reason, in the same manner as in the conventional formatting method, in the next rotation, only the identification information for recording is checked, so that formatting can be completed with a smaller number of movements (rotations) than the method in which the identification information for reproduction is written during the third rotation after the next.
According to an aspect of the present invention, in a magnetic disk apparatus which uses a dual magnetic head and changes the position the magnetic head for recording and reproducing operations, and under a system of separately providing identification information for recording and identification information for reproduction, designed not to deteriorate the accuracy of detecting an address division when positioning the magnetic head for recording or reproduction, the identification information for recording and the identification information for reproduction are respectively added with an ECC code and an identification area for recording is placed ahead of an identification area for reproduction, and therefore, a little leeway is provided for error correction between the recording identification area and the data area, and when writing data, after errors of the identification area for recording are corrected by ECC, data can be written in the data area placed physically in the same sector without deteriorating the formatting efficiency. It ought to be noted that even in the case where an error correcting code is not added, an effect is offered that the formatting efficiency is high because no gap is required behind the recording identification area.
According to another aspect of the present invention, while errors of the identification area for reproduction are being corrected by ECC, data is stored in the FIFO unit, and after the correction by ECC is finished, and if the identification area for reproduction accords with an object identification information, data is transferred from the FIFO unit to the data buffer, and if the identification information for reproduction does not accords with the object identification information, the data in the FIFO unit is invalidated, and therefore, when reading data, after errors of the identification area for reproduction have been corrected by ECC, since no area needs to be provided to gain time, data can be read from the data area placed physically in the same sector without reducing the formatting efficiency.
Further, according to yet another aspect of the present invention, since the identification area for recording is placed physically ahead of the identification area for reproduction, time can be secured for the maximum likelihood decoding (e.g., Viterbi decoding) and a digital signal process between the recording identification area and the data area, when writing data, after the maximum likelihood decoding of the identification area for recording and the digital signal process are conducted, data can be written in the data area placed in the same sector without reducing the formatting efficiency.
According to a still further aspect of the present invention, since the identification area for recording is placed physically ahead of the identification area for reproduction, when an identification area for reproduction is to be recorded during formatting, before that, the identification area for recording is read and the identification information for recording is compared with an expected value and its adequacy is checked, and after this, an identification information for reproduction can be recorded during the same rotation, with the result that the formatting time can be reduced and moreover, the reliability of the identification areas can be enhanced.
The fourth and fifth objects of the present invention will be described.
According to a technique revealed in JP-A-3-160675, there is a problem in the down-sizing and capacity-increasing of the magnetic disk unit. Because it was necessary to provide twice as much servo information and ID information as in the case where a single head is used both for reading and writing.
The presence of twice as much servo information requires to used an expensive servo writer or formatting the magnetic disk which has to be occupied for a long period of time. Because the format process using such a servo writer continues for long time, the production cost of the magnetic disk unit increases and it is difficult to provide a less expensive disk unit, which has been a problem.
The fourth and fifth objects of the present invention are to solve this problem.
In order to achieve the above object, according to the present invention, there is provided a disk type recording and reproducing apparatus comprising a disk type recording medium, and a dual head including a reading head for reading from the disk type recording medium and a writing head for writing into the disk type recording medium, wherein the disk type recording medium having a plurality of recording tracks, each track having a plurality of sectors, wherein each of the sectors has an data division and an ID division provided ahead of a data division disposed in the circumferential direction of the disk type recording medium, wherein the ID division has recorded thereon identification information of the sector, wherein the ID divisions are provided in positions shifted with respect to each other in the radial direction of the disk type recording medium by the amount of shift between the core centers of the reading head and the writing head, and wherein the data division has identification information of the sector stored is placed in a position ahead of data to be recorded and reproduced.
According to an embodiment of the disk type recording and reproducing apparatus, by providing only a servo area for reading, the memory area of the disk type recording and reproducing apparatus can be utilized to store user data. In this case, to read data, the dual head has only to be controlled such that the reading head is positioned to the center of the track. To write data, it is only necessary to realize control such that the reading and the writing heads of the dual head offset-positioned by the amount of shift between the two heads with the reading head positioned to the center of the track. Meanwhile, if head positioning is done in the range where the linearity of the position signal cannot be maintained, the accuracy with which the magnetic head is positioned to a target position deteriorates, and the track density cannot be increased. So, considering the linearity of the position signal, both the write ID area and the read ID area may be positioned offset with respect to the position signal.
According to this embodiment, both ID areas for writing and reading are provided, but, since ID information for reading is recorded in the data area, in contrast to the case where the ID division for reading is provided independently of the data area, the SYNC area, etc. required to read the read ID division can be removed, so that the storage space for user data is increased.
In this embodiment, the ID divisions need to be recorded on the recording medium by being shifted with respect to each other accurately by the amount of shift between the core centers of those heads and under this condition, offset positioning of the heads is performed. When writing servo data, if a laser length measuring system is used to record the ID divisions, the ID divisions can be recorded in accurate positions and the heads can be offset-positioned in the accurate positions. Also in this case, if the area for ID information and the data area are placed taking the range of linearity of the position signal into consideration, the track density can be increased, and the capacity of the disk type recording and reproducing apparatus can be increased, so that and it is possible to provide a large-capacity disk type recording and reproducing apparatus.
Moreover, when writing servo data, data is recorded on the medium by completing one track after another, but owing to a blur in writing between the adjacent tracks, in case positioning the reading head, there is a possibility that the track center deviates a little from where it was when servo data was written. In anticipation of such a case, if a pattern for measuring a shift between the core centers is recorded on a specific track of the medium and if this pattern is read with the reading head and the writing head, the value of shift between the cores can be measured, and by writing the ID division based on the value of shift, offset positioning of the heads can be achieved.
According to another embodiment, the apparatus is provided with another head with a core width which covers the circumferential widths of the writing head and the reading head, for example. With this head, the ID area is recorded on the medium. By this arrangement, recording the ID area on the medium or rewriting the ID division in the alternate sector process, for example, can be finished by a single operation, so that high-speed processing becomes possible.
According to the present invention described above, it is possible to provide a disk type recording and reproducing apparatus of a large capacity and a small size. The present invention has been described taking the magnetic disk unit for example, but the present invention can be applied to disk type recording media in general, including the optical disk.